Transformer Objective Type Question Answers

41. The impedance seen by the primary in Fig. 5 is 

(i) 5 Ω
(ii) 25 Ω
(iii) 625 Ω
(iv) none of the above

42. The primary current I_p in Fig. 5 is 

(i) 2 A
(ii) 0.04 A
(iii) 0.004 A
(iv) none of the above

43. The voltage across 40 KΩ resistor in Fig. 5 is  

(i) 1000 V
(ii) 500 V
(iii) 800 V
(iv) none of the above

44. The voltage across 20 KΩ capacitor in Fig. 5 is  

(i) 200 V
(ii) 400 V
(iii) 1000 V
(iv) none of the above

45. The secondary current I_s in Fig. 5 is 

(i) 1.25 A
(ii) 50 A
(iii) 0.02 A
(iv) none of the above

46. Cores of large transformers are built upto nearly circular cross-section in order to reduce 

(i) leakage reactance
(ii) iron losses
(iii) eddy current loss
(iv) copper loss

47. The core-type transformer provides 

(i) much longer magnetic path
(ii) shorter magnetic path
(iii) lesser average length per turn
(iv) none of the above

48. The core-type transformer is generally suitable for 

(i) high voltage and small output
(ii) high voltage and high output
(iii) low voltage and high output
(iv) none of the above

49. Transformers having ratings less than 5 k VA are generally  

(i) oil cooled
(ii) natural air cooled
(iii) water cooled
(iv) none of the above

50. The transformer that should never have the secondary open-circuited when primary is energised is 

(i) power transformer
(ii) voltage transformer
(ii) auto transformer
(iv) current transformer

51. The temperature rise of a transformer is directly proportional to 

(i) apparent power
(ii) reactive power
(iii) leakage reactance
(iv) none of the above

52. In an auto transformer, the primary and secondary are ………. coupled.

(i) only magnetically
(ii) only electrically
(iii) magnetically as well as electrically
(iv) none of the above

53. The impedance reflected back to the source in Fig. 6 is 

(i) 11.2 Ω
(ii) 22.2 Ω
(iii) 25 Ω
(iv) 47.8 Ω

54. The secondary load impedance of a step-up transformer is Z_s The primary impedance will be

(i) equal to Z_s
(ii) greater than Z_s
(iii) less than Z_s
(iv) none of the above

55. The steel used for transformer core has

(i) high silicon content
(ii) high permeability
(iii) low hysteresis loss
(iv) all of the above

56. In a transformer, leakage flux

(i) helps in transfer of energy
(ii) is negligible at full-load
(iii) is minimised by interleaving the primary and secondary windings.
(iv) produces mutually induced e.m.f.

57. Short-circuit test of a transformer helps us to find its

(i) iron loss
(ii) full-load Cu loss
(iii) Cu loss at no load
(iv) none of the above

58. A two-winding transformer operates at maximum efficiency when its

(i) hysteresis loss equals eddy current loss
(ii) Cu loss equals iron loss
(iii) primary resistance equals secondary resistance
(iv) voltage regulation is minimum.

59. The all-day efficiency of a transformer is also called its

(i) energy efficiency
(ii) power efficiency
(iii) current efficiency
(iv) none of the above

60. The short-circuit test helps us to find

(i) Cu loss at any desired load
(ii) iron loss at no load
(iii) Cu loss at no load
(iv) none of the above

61. The power efficiency of a lighting transformer is always ………. its all-day efficiency.

(i) equal to
(ii) higher than
(iii) less than
(iv) none of the above

62. With a load of leading power factor, the full load secondary voltage of a transformer is ………  its no-load voltage.

(i) equal to
(ii) less than
(iii) greater than
(iv) none of the above

63. What is the approximate efficiency of large transformers ?

(i) 65 %
(ii) 75 %
(ii) 85 %
(iv) 95 %

64. An isolation transformer has primary to secondary turns ratio of

(i) 1 : 1
(ii) 1 : 2
(iii) 2 : 1
(iv) can be any ratio

65. The load on a transformer is 2 ∠0^o Ω or  2 ∠20^o Ω. The efficiency of transformer will be

(i) greater for a load of 2 ∠0^o Ω
(ii) greater for a load of 2 ∠20^o Ω
(iii) the same for two loads
(iv) data insufficient